The Parametric Study of the Crack Growth in the Lubricated Rolling-Sliding Contact Problems

Abstract:

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A two-dimensional numerical model is used to describe the crack path in the lubricated
rolling-sliding contact problems. The model assumes that the crack is initiated in a pre-existing
micro pit, which resulted from the crack growth on the surface of a gear tooth flank. The lubricated
rolling-sliding contact problem is modelled using the Hertz theory of contact, the Coulomb's law of
friction and hydraulic pressure mechanism with constant pressure which simulates the effect of
lubricant trapped into the crack. Different load cases are used to simulate the moving of a contact
load. The crack propagation path is evaluated by a maximum tangential stress criterion and
modified maximum tangential stress criterion which considers the stress intensity factors KI and KII,
the T-stress, the critical distance ahead the crack tip rc, and the stress on the crack surfaces. The
computational results show that the consideration of the T-stress has a significant influence on the
crack path in the lubricated rolling-sliding contact problems.

Abstract: Multi-crack problems are deeply involved in rock-like material and rock engineering. In order to study the influences of lateral stress and inclined crack angle on the failure load of the multi-cracked body, uniaxial and biaxial compression fracture tests are conducted on plate specimens with regular distributed multi-cracks. The stress distribution and the stress intensity factors KI and KII for every crack tips of the specimens are calculated by FEM. The experiment revealed that the failure load of the multi-cracked specimens increase obviously with the increase of the lateral pressure σ2 and the inclined crack angle α. And the multi-cracked specimens will hardly initiate propagation under equal biaxial compression. Analyses have been shown that these can be explained by the variation of KII with the σ2 and the α.

Abstract: A two-parameter constraint-based fracture mechanics approach is used to explain the effect of the constraint on the apparently anomalous behavior of short fatigue cracks. The different levels of stress constraint are quantified by the T-stress, and microstructurally as well as mechanically short cracks are discussed. Short cracks generally behave more sensitively to the constraint than the long ones. It is shown that in most cases, the existence of short cracks goes hand in hand with an intrinsic loss of the constraint, which contributes to a decrease of their fatigue
threshold values and accelerates their growth. In this paper, the above effect is quantified and conclusions concerning the applicability of the fracture mechanics parameters and approaches to the estimation of the residual fatigue life of structures are discussed.

Abstract: Fatigue crack growth under mixed mode loading conditions is simulated using S-FEM. By
using S-FEM technique, only local mesh should be re-meshed and it becomes easy to simulate crack
growth. By combining with auto-meshing technique, local mesh is re-meshed automatically, and
curved crack path is modeled easily. Plural fatigue crack problem is solved by this technique. For
two parallel crack problem, criteria of crack coalescence are proposed. By simulating this problem by
S-FEM, it is verified these criteria are conservative ones.

Abstract: The wedge splitting (WS) test is now a promising method to perform stable fracture mechanics tests on concrete-like quasi brittle materials. Fracture parameters, such as fracture toughness and critical crack opening displacement and et.al, are however not easy to determined since formulae available from stress intensity factor manual are restricted to standard specimen geometry. The paper attempts to compute expressions for commonly used fracture parameters for a general wedge splitting specimen. By means of finite element analysis program, test simulation was performed on non-standard wedge splitting specimen with different depth and initiation crack length, and thereafter expressions were proposed for stress intensity factor at the pre-cast tip and crack mouth opening displacement on the load line. Based on the work above, size effect on the unstable fracture toughness and crack extension were investigated, and the consistency of fracture toughness data for various specimen depth as well as initiation crack length is demonstrated. The crack extension is little sensitive to the initiation crack length, it increases with the depth of specimen, which can be explained by the boundary influence of the specimen.

Abstract: Based on the theoretical study on the tip stress intensity factor (SIF) of the crack normal to and dwelling on the interface, using the finite element software ANSYS, the SIFs of the double interface cracks normal to and dwelling on the interface in cladding material structure are studied by changing the crack spacing, the crack length, the cladding thickness ratio, the load and the crack location. The results show that, the crack SIFs become larger with the increase of the crack spacing, the crack length and the load, they become smaller with the increase of the coating thickness ratio, that the SIF of the crack close to the boundary becomes smaller with the increase of the distance between the crack and the boundary, and that the SIF of the crack in the middle of the interface becomes larger with the decrease of the crack distance.